Aircraft control system



Dec. 15, 1953 W. H. GILLE AIRCRAFT CONTROL SYSTEM Filed Feb. 2l, 1947 2 Sheets-Sheet l WILL/5 H. G/LLE Dec. 15, W GILLE AIRCRAFT CONTROL SYSTEM 2 Sheets-Sheet 2 Filed Feb. 2l, 1947 INVENTOR w/LL/S H. /LLE Patented Dec. 15, 1953 AIRCRAFT CONTROL SYSTEM Willis H. Gille, St. Paul, Minn., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application February 21, 1947, Serial No. 730,022

The object of this invention is to provide a new flight control system for an aircraft.

There is apparatus in existence for stabilizing an aircraft in flight about its turn, its roll and its pitch axes. The aircraft in flight by such existing means may be made to y in a level position in a desired heading. However, despite such stabilizing means the aircraft may nevertheless be proceeding through the air in an undesirable attitude. By undesirable attitude is meant that the aircraft for example may be skidding through the air although headed in the desired direction. This skidding position may be due to poor directional stability of the aircraft in flight.

It is known that the tail surface of a conventional aircraft due to the streamlining action of the air thereon causes the aircraft to act as a weathercock when in night and thereby tends to cause the aircraft to head in the direction in which the aircraft is moving. The tail surfaces thereby tend to increase the directional stability of the aircraft. However, such action by the tail surfaces is not completely effective to eliminate this skidding action. The aircraft will, notwithstanding, be at times headed in a different direction from that in which it is moving in the air. The existence of a difference between the direction of heading of the aircraft and direction of movement of the aircraft in air implies that the aircraft is in a condition that is generally known as in yaw. Whenever the aircraft is not headed in the direction in which it is moving relative to the air that impedes its movement it is therefore said to be in yaw.

In one type of aircraft which has no tail surfaces such as in a tailless airplane the directional instability of the aircraft is greater than that of the conventional type of aircraft that is equipped with a tail. Such tailless airplane which is popularly known as a Flying Wing consequently tends to y in a condition of yaw to a greater extent than the conventional airplane.

It is an object of this invention to remove the yaw of an aircraft in flight by the operation of only the rudder of the aircraft, the ailerons being unoperated at this time. The operation of the rudder is adapted to cause the aircraft to head in the direction in which the aircraft is moving. By such operation of the` rudder the aircraft tends to align or streamline itself with the direction in which it is moving.

The flight control system that is the subject of this invention further provides a device which detects when the aircraft is in yaw. This yaw 16 Claims. (Cl. 244-77) detector in turn controls means for operating the rudder. This rudder operation causes the airplane to head in the direction in which it is moving.

When it is desired to change the direction in which the aircraft is moving, the ailerons of the aircraft are operated to effect such change. The direction in which the aircraft is moving is changed by the operation of the ailerons whose operating means for this purpose is placed under control of a deviation responsive means and the yaw detecting means.

The deviation responsive means indicates when the aircraft is headed in a direction different from that previously selected or desired. The yaw detector indicates when the aircraft is headed in a different direction from that in which the aircraft is moving. As long as these indications are the same, the aircraft is actually moving in the desired direction and the ailerons are not operated, but the rudder being under control of the yaw detector is operated to remove the yaw thereby removing both the yaw and the deviation indications. However, when the yaw indication and the deviation indication are not the same, the aircraft is not moving in the desired direction. The yaw indication and the deviation indication thereupon differentially control the operating means for the ailerons which causes the aircraft to bank. The effect of the bank causes the aircraft to turn so that it assumes the desired direction of heading.

A vertical gyroscope is provided which controls means to stabilize the aircraft about the pitch and roll axes of the aircraft and to aid in effecting the proper attitude of the aircraft While it is turning.

An additional gyroscope in one embodiment of the invention coacts with the yaw detecting device in the operation of the rudder to prevent oscillations of the aircraft about the direction it is moving when the rudder is operated to remove yaw.

By the means to be described therefor a novel system of controlling the aircraft in flight is set forth. In this system the function of the rudder which in existing systems had been operated to change the direction in which an aircraft was moving is herein operated only to cause the aircraft to head in the direction in which it is moving. The above function of changing the direction in which the aircraft is moving is no longer in the rudder but in this system to be described has been incorporated in the ailerons.

In the existing systems of flight control, the

.. :.aignt-througli-ftucisets c.

. .of .esem/.matin sin. operati@ aeeavoe is moving is changed to prevent skidding in La turn. In old systems When the deviation responsive means gave an indication irrespective-'orante tWo causes of deviation cited theiailerfonsa vwell as the rudder Were operated t th! f aircraft to head in the desired case or to cause the airplariedtomovfe in the dsired direction in the other Afcase. 'Thisiperat'ion of the ailerons along with the operationo f t he rudder causes the airplane to be banked unneces` 'ldirctionaliglyro. .the heading A.W..S.-. the( .movement .but this?? plane with lits' flights; ...Salts in. the .ballkilg Of fact 'that'the hn' .indication inthe.-

;tion does not of s elfc n troltlie! barilringfof 'the ;aircraft` L. he aircraft' is therefore f not unnecesbedirec- ..Flightcontrolsagn neweconccptiofi-COI-l will g aircraft. inj night 11,11%n agt'alle'ss'iairfria. 'The .fanless y notg have a "tail 4liv-icc'. Of. 'airipulatedin which it is mounted. A turn in e1ther`d1rection onetime. f-Forexaglpla' lilfr nalfiightlit'is the closing th tive position.

The other set of control surfaces controls the movement of the aircraft about both the pitch and the roll axis. This set of control surfaces must therefore act as the conventional ailerons in tilting the plane about its roll axis and also in moving the plane about the pitch axis which is conventionally effected by elevators. The set of control surfaces comprisest-Wo 4control surfaces. One surface is mounted'in each wing, zA control A`.system has been devised whereby at times these tvvo control surfaces move in the same direction' to act asel'e'vators The control system functions on otheroccasions to move the control surfaces in opposite directions which movement corretothatf'given the conventional ailerons.. Sincethese'control'surfaces have both an elevat'or Ian`d"an "aileroneffect on the aircraft, they have beenv designated elevons.

"`A further object of this invention is to provide means incorporated in a flight control apparatus for 'separately controlling the positionl of tvvo'control surfacesflforfarriaircrafteach-ef Which-effects movement of theaircra'ft Vaboutthe#sainefaxis.

j A further object 'ofithisiinvention is'ltop'rovide 4means incorporatedin an automatic --iiightucon- 'trol system;forfconcrriitantly adjusting twolcon trol surfaces whichv` 'control the niovementffofitlie aircraft yaboutfthe rollaxis; intheV saniedirection.

A further Vobj ect off this' inventionis-to provide means man automatic flightcentrol systems-for concomitantly adjusting Vtwo con-tr" #surfaces whichcontrolthe movement of the aircraft about the pitch axis; in opposite directions.

' Other objects'and advantages ofth-islinvention Will become apparentV from ya cons' tion-lof the specification Att` gether Withl the drawings showing embodiments of the'l invention" or as# hereinafter pointedv out in the4v claims.

. 4In thedrawings:

, Figure l illustrates *flight control apparatus Which embodies thenew principle of controlling an aircraft 'in 'flight as adapted -to the-'convenfnew principle of continuing an aireraftfirilaigm as 'adapted to atai'lless airplane.

` Figure 3' shows an arrangement -ffor damping the movementsiof the vane.

Apparatus for ga'utomatically controlling'l1the flight' of ay conventional aircraft -Will be c'ons-id ered in thejiirst instance. The conventional-faircraft 'when' inf flight is controlledy about its; turn ,axis byr a grudder, about its roll axis b v-y ailerons and about its pitch axis' by elevators. eral control surfaces are operatedifrom f con'trol channels fvvhich. .are'so injdicatedjirr Figure 1. In

' Figure 1 the ruk-ljder,` aileron and elevator-"control channels -are illustrated vrespectively from-'leftto A right. The respective channels win lb' described in' this meer.

V.The ruddercontrol surface, Whichis notisliovn L isoperated by cables Ii extendingifrom the'cable 'moter- 3 by may reversiblvwdrvrshaft |2" andthe motor-'fis cable drum Il' is drivenby servojjSAer'vomotor Y I3 drum H. TheA ears i 'shaft )12.

i' er I (i`- may also of the' type "disclosed l"in: .the vabove noted application. The .direction .ofrotacurrent suppliedA to amplierl from a'source 'of turn indicator.

cator has a cardan ring which is supportedon |00.' The source |00 may be an inverter not shown or any other suitable source of alternating voltage.

The control signal to the amplifier I6 is obtained from a circuit including a series of connected networks 30, 50 and 10. The signal circuit extends from amplifier input lead 20, impedance network 30, lead 4|. impedance network 50, lead 60, impedance network 10 to ground 84 and to ground 90 of amplifier 60.

The impedance network may be designated the circuit balancing network and is in the form of a Wheatstone bridge. Two legs of this bridge are formed by a centering resistor 3| whose opposite ends are connected by leads 32 and 33 to the ends of a secondary 34 of a transformer 35. The primary of the transformer 35 is connected to the source of voltage |00. Since the several networks to be described have secondary windings that may have a common primary winding, the primary winding is indicated in each instance by the reference character 40. The opposite two legs of the Wheatstone bridge are formed by a servo balance resistor 36 which has its opposite ends connected through leads 31 and 38 to the respective ends of secondary winding 34. A wiper 39 may be manually adjusted along the surface of resistor 3| and a wiper I4 which is connected to the amplifier input 20 may be adjusted along the surface of resistor 36. The wiper I4 is driven from the servomotor I3 through a follow-up connection I1.

Wipers I4 and 39 are normally at the electrical centers of their respective resistors. When so positioned, the wipers I4 and I9 are at the same potential and no voltage signal exists between these wipers. If wiper 39 be manually displaced from its electrical center in one direction or sense, wiper I4 must be displaced by the same amount in the same direction or sense in order that the wipers I4 and 39 be at the same potential so as to provide no signal voltage between them. Wiper 39 may be adjusted by hand as desired and wiper I4 must be similarly moved to a point of equal potential with respect to wiper 39 to balance network 30. Since wiper I4 is connected to the driving means for the rudder, the adjustment of wiper I4 will alter the position of the rudder. Wiper 39 may therefore be variously moved to unbalance network 30 and the adjustment of wiper I4 to rebalance is also effective to position the rudder where desired, but it is generally adjusted so that the rudder is in center position. For this reason wiper 39 with its resistor 3| are often termed the centering means.

The impedance network 50 is a source of angular rate signal and has its operative portion in the form of a potentiometer. This potentiometer comprises a resistor 44 whose ends are connected through leads and 46 to the respective ends of the secondary 41 of a transformer 48. The primary 40 of transformer 48 is connected to a source of voltage |00. A lead 4I extends from wiper 39 of impedance network 30 to a center tap 42 of resistor 44. A wiper 49 may be adjusted along the surface of resistor 44 with respect to center tap 42 to vary the potential between the wiper and center tap. The wiper 49 is normally at center tap 42 but is adjusted relative thereto through an operative connection 53 from a rate gyro 54.

The rate gyro 54 may be a spring restrained gyro similar to the conventional gyroscopic rate Such gyroscopic turn indi- 6 horizontal trunnions extending from the ring. The precessing action of the gyroscope when the aircraft is turning about its turn axis causes the rotation of the trunnions. Such rotation of the trunnions may be applied through mechanical connection 53 to wiper 49.

A lead 60 extends from wiper 49 to a center tap 11 of a resistor 1| which forms part of vane controlled impedance network 10. Impedance network 19 includes a potentiometer whose resistor 1| has its opposite ends connected by means of leads 12 and 13 to the respective ends of a secondary 14 of a transformer 15. The primary 49 of the transformer 15 is connected to source |09. A wiper 18 may be positioned along the surface of resistor 1| with respect to center tap 11 to vary its potential with respect to the center tap 11. The wiper 18 is so positioned from a vane through an operative connection 19.

The vane 89 may be similar to the type shown in Patent 1,119,324 dated December 1, 1914. Such vane is adapted to pivot by the action of the airstream thereon. The extent of vane movement is a measure of the differential air pressure on opposite sides of the fuselage. Any pivotal action of the vane is transmitted through the operative connection 19 to the wiper 18. Wiper 18 of network 10 is connected to ground 84 and is therefore common with ground 90 of amplifier I6.

The vane may have its shaft 19 damped by a conventional dashpot to prevent oscillations of the shaft or the shaft may be operated by a gyro which is slaved to the vane similar to the slaving action of a gyromagnetic compass.

The ailerons, not shown, of the aircraft are connected to cables III) which are driven from cable drum IIi. Cable drum II I is reversibly driven by servomotor i I3 by means of shaft I I2. servomotor IIS is similar to the servomotor i3. servomotor ||3 is reversibly controlled from an amplifier IIS through its connecting leads H5. Amplifier H5 is similar to amplifier I6. The control signal for amplier IIB is obtained from a circuit extending from lead |20, network |39, lead |4I, network |58, lead |63, network |19, ground I 84 and to ground |90 of amplier II 8.

Input lead |29 from amplifier IIO extends to wiper ||4 of the impedance network |30 which is designated the circuit balancing network. The impedance network |30 is in the form of a Wheatstone bridge. Two legs of this bridge are formed by a centering resistor |3I which has its opposite ends connected through leads |32 and |33 to the respective ends of a secondary |34 of a transformer |35. Transformer |35 has a primary winding 40. A wiper |39 may be manually adjusted over the surface of resistor i. The other two legs o1' the Wheatstone bridge are formed by a servo balance resistor |39 which has its ends connected through leads |31 and to the respective ends of secondary |34. The wiper |14 maybe positioned along the surface of resistor |33 through a follow-up connection I|1 from servomotor II3. Wipers II4 and |93 are normally at the electrical center of their respective resistors |35 and |3I. If one wiper be displaced from its electrical center the wipers I I4 and |39 will not be at the same potential and a signal voltage will be derived due to the difference in potential. Wiper |39 may be manually adjusted along resistor |3|. The movement of wiper I|4 which is necessary to place wipers |39 and I|4 at the same potential is also applied toV the ailerons not. shown.. Wiper |39 of .secondary IFM.

may thereforez :.-incme'df 1 to.l .unbalancegnetwnrk 1.3.0 andhtheemovement of miner met :tomaia-nee the :network: 'Tis effective: :toy fthe anormal positionvoithe ailerons. Generallythe ailerons are. .adj usted; iint'o: vther centra-1v positionY and las so used the wiper ISS? wrtlrsits: resistor :flint-.is termed. :the centering means-inutile: ailerons.

"Iheflea-drIltl.i extendstrom wiper-:lf3 intera-f. wiper 1.58.. The .impedancemetwnrkz l-i: awhieh- -issithe transverse :stabilizing: network :and which :in-.- cludfesr-wiperulliaeompriseszga `resistor. I5I whose opposite.. rareconnected: through leads` 1h52 and 153" to.`v thezzrespective ends otfa-.;s.econdary windingilit of a.'transfnrmer"l=5i Th-e1 transhettrositionert:'along'athez .surface of, resistor f1I5rI and :receivesisuchimovementfrmmaivertical' gyro 46st :throughaan operative comieetiorr .162. 'Ehe vertical gym Eil-at may ibeffof'zfthez .type'fdisclosed in my aforementioned application Ser. No. 447;,.- 989.. :The movement anplied .ter connection.'- fI 62 .trom the .vert-ital: erro @ilk-Git fresuts1fromf-more mentlnf 'the.z-ai'rcra-itabout-its rGl1-.,axis-.. .Bes-istol- :tt: :has-:a center tapfrlilgand in `normal posi.- tionnwiperr I;5& isatfthefeenter ,tapx :I'zmay'be fdisnlacedxtoaeithertsidaotieenter tap Iiil rand. when :so: positioned fitr .ha-lt cycle wouldv seleet gpo'sitine ser' )negative voltage with respect to the :center tap. Fliheeenter :.tapr lL60 is comieetedfthrouglr lead ..I(3.-to .a.-,Wiper ,I'I.f.5.-.of a flight ldirection. .controlA impedance `.network .IIIJ- The `Vinipedanee. network .'I-1.Df;isin .,theeformof `a Wheatstonefbridger Twee legsothis bridge are formed .byzavane :responsive .resistor mi .whosev opposite .ends .arefeonneetedt throughdeads .I v'lg8yand 'H9 totherespectiveends. oifasecondary -Ifmof ,fa :transformer .'I '1.52.v The .transformer .H5 .has "a primary .40; The "other two .legs of .this .bridge .are- '.formed by 'a direetien'ali.` etz-ro. .responsive resistor Ii1l= VWhoserespective ends .are .con- .nested `througlti .leads .EI-12: and; 1h13'4 fto the `ends VS/iper. M61 may-ubs positioned falong .the surf-ace@ of mesistor HI.; .-Such. posi .tion fis. obtained :from la directionah gyl@ `l|32 through olgierative :connection 18.3... The direetional gyro .may fbe of. the'ftype ,disclosed- .application Ser; .Nm .4M-MM; mentioned-above.

.A vwiper. I Bil-may rbpositioned along. the: surface of resistor 17H. lllhemositioning ot wiper. .I-S .fis

obtained'. from vane 80; :throughV 4an Loperative f .connection 118|. Wiper YI8I1-isi fconneeted .to ground; IBA...

.The elevators; fnot shown, `:are .eonnected to cables 2m. fCaloles` e210; tare :driven .-.from the driven from a servomotor Y21.3 bmmeans'.- of 'roperative connection 242; servomotor .2.t3. is reversibly controlledl from aan'. `amplifier 2k6 `through leads 21:5.. .Theamplier L6 'ia-ndserve- ,motor 2I3. are .similar .to those-inthefrndder .and aileron control.; channels. fIT11eir1 putv signal for controlling thexamplifier ZI-.isderivedrirom a controlcircuit .which .extends from-.'innut :lead 222i) of the ampler, impedanceiinetwork 12333.

llead 24|, vimpedarnze.:neinavorl: lead-251, .lim- "f f' extends to wiperfilsof atlongitndnalsstabi'lizing impedance. inetworlc :230. impedance; network 230'. comprisesa-resistor L23 I. haring its/nop- .posite ends. .connectectfthrough fleads112 32; 233.1120 :the respectve==ends1of aiseoondaryahot astransformerf2'35. .'Theitransfomerinirlasaprimary winding .49.1 wiper- 123?! may-'tbe positioned alongcthe surfaaez:of'-.resistor del. The winervfl is driven from vertical gyro ISI throughnoperai'fn/e:lconnedtionl 5.2.40. Thea .movement given; to wiper23t15fronr. gyra. .IIGIQ is the-:resultof vmovement :ofi thefgaireraftrabout its piteh axis; The resistor 1231i. has.: a zeenter :tap 2;38. `Normally Winer i231. zia-:positioned atthe center. tap. .The wiperfzt: may beamoved inv either. direction with respect to the center-tap,v and in any. halteyele, its.potentialnwithrespect oto the center. tap; y238 Maries ywith :its fdirectiontof. movement .relative thereto.. Y

The eenter tapfz-23-3 -is connected throughalead 2M '-toi-wiperdd ofu pv elevator .impedance .net- Werk 1250.. impedance network 250. comprises@ resistor r251|- zhaving; one: rend conneotedthrough lead.f253=:to onelend of-.se.co1idary2 5dr ofeav .transformerz; The transformer .zfhasa primary 4.0;. ,The-.oppositeendgot-resistorzl is-conneted threiigh.;aflead-.itsto lead- 253: so that bothtends of resistor .2;5 I: pare :connected-1 to` vthe same. end offseoondaryt. .The opposite-.end oiseeendarwlz'd.. is 'connected :through a;.1ead;2 52- to: auenteratapi-.S-ot resistorll :and through. lead lr25'! to. a y.wiper :2.60 f. of. a. control.. circuit balance .net workfli.. -Wiper 12d# iSfnOrmally positioned-aat the. center 'atan `to:resistor V25 I- when. ,theyv .are at. thesamBtpQtentiaI. :'It may .he seen that :in any Ihal cycle and for Vgiven..mm/zernent that irrespective fof the Adirection which-wiper 24.4 is moved .with-;respent.toits-center tap 25.6Y the difference .of potential. between wiper v`Zlilwand center tap 25E fisifthe: same;

lhef impedanceinetwork 6l awhioh 4eonstitaites the controll eircuitrebaianoing :networki is :inthe formnfaaillheatstonewbridge.. "Two legsof-4 the bridge. are. .formed :byza `resistm 216:2 whose; opiposite. ends .fare conneted through-leads12 6:3.; and 2F64 to. `thefresloentivefends of: .a secondary .1265 .of af. transformer 'Il'iegtransformer 266:.has a primary:awindinge'fdli. An adjustable wiper 26.0 contacts.v the.. surface .ofi resistor? 26,2. The-,other twolllegs. offth'e. bridge; afrezformed byy a Ysert/io balance resistor 2216:' whiohihasv sits- .oppositeen'ds connected 1to the respective ends. fof secondary 2te throughlearis @15,5212. A'WiperZ-Mwmay be manually adjusted' over: the'. surfaeeofv :resistor @T92 llhewiperilsdis eonneoted'to ground-284.

The/wiper :2.6.9: previously. mentioned y'is driven fromlthefollow-upiconnection If extendingsffrom 'servomotor2l3.. VWipers Zyand 2M- are nor.-

malty at. the electricalcentersgof ftheirLrespe'ct-ive resistors :1252i and' 2?0.. When in such position the wipers .land. 2J d1 arexat the: sameipoten- Wiper 211e may he vmanually adiusted at tionoff wiperA Zf'l, in. orderathatpno potential dif:-

grferent-:eexist Abetween: .the wipers 2M: .and Y260,

such movement of-wiper .lfis alsoiappliedto'the elevators notsh'own. Wiper ZI'danclfresistor 211:0 `arey therefore designatedtthezcenteringmeans :for

the-elevators. The various elements areishuwn' the drawing in' tlie1positionithey assume `.when :theplane `is-*dying .in the. direntionvinA which .it is desired -toflyranol isi also headedginthat direction. This :is theeoonditionnwhichis desiredto maintain.

Under' these: conditions-, the lser-ies of. networks nonneetedlto) eachyofv :the Vamplifiers `|16i .II-6 vand 2I6 is balanced so that the servomotors .I3,.. I.I:3

,:an1.;;2.li3=remaindeenergized. Thus, referring to the rudder cont-relfchannel, it will. be. noted that slidersrtllandz'narboth.-iat corresponding'fposi- 75 tionsfiwithirresnect to;;rre sistors; 3.6 IVand. 3.! i `so that no voltage exists between these two sliders. Similarly, slider 49 is adjacent the center tap 42 so that no voltage exists between slider 49 and center tap 42. Similarly, the voltage across net- Work I has a zero value. Considering now the aileron network, it will be observed that the bridges i3d and ll are balanced and that the slider H53 of network It is adjacent the center tap I6@ so that no voltage exists between slider |58 and tt. Thus, the various component networks of the series of networks controlling the aileron are all balanced so that no voltage is supplied to the input of ampliner I I 6. A similar condition exists in the elevator control channel. The bridge 26| is balanced and the slider 23? of network 23e is at the center tap 233 of resistor 23I. In the network 258, the slider 244 is at the center tap 256 and is hence at the same potential as the left-hand terminal of secondary 254 to which lead 25? is connected. Thus, again, the various networks connected to amplifier 2I6 are all balanced so that no voltage is supplied to the amplifier it.

Operation Assume now that the plane is still iiying in the direction in which it is desired to ily but that the heading of the aircraft is changed so that it is not headed or is not pointing in the direction in which it is moving. In View of the fact that the aircraft is headed in a different direction from that in which it is moving, the

vane 8E of the aircraft will be rotated by the streamlininnr action of the relative air upon it. The movement applied to vane 8G by the relative air is transferred to wiper 'I8 of the rudder control network and the wiper E80 of the aileron control network.. rThe directional gyro I82 responds to change of heading of the aircraft with respect to the desired direction of heading which in this case is the direction in which the plane .is moving. The directional gyro through its operative connection |83 therefore displaces wiper l in an amount proportional to the diierence between the desired heading and the present heading. In the present case the displacement of wiper HS by the directional gyro is in the saine direction and is of the same amount as the movement applied to wiper $30 from vane S. No difference of potential therefore exists between wipers iSd and H6 and no control signal "is applied to amplifier liS of the aileron control channel.

Howevery in the rudder channel, the displacement of wiper i8 with respect to center tap 'i1 of resistor l! of network 'le causes a control signal to be set up which is applied yto amplier I6. The amplifier IS as shown becomes operative to control the direction of rotation of servomotor i3 in such a direction as to move wiper I4 through follow-up connection I'I. The movement given to wiper H is in such direction and continues until it has set up a difference of potential between wiper I and. wiper 39 equal and opposite to the voltage existing between wiper 'I3 and center tap Ti. At such time, the amplifier 5 no longer receives any voltage from the networks and ceases to cause operation of motor It. The movement given to wiper I4 from servomotor I3 through follow-up means I'I is also applied `through operative shaft i2 to cable drum II. :The cable drum I therefore positions rudder fthrough cables it, The airplane turns under the :effect or" the'rudder and the turning action of the Lplane causes the .rate gyro 54 to apply movement 10 to wiper 49. The direction in which wiper 4S is moved by the rate gyro is such as to set up a voltage between wiper 49 and center tap 42 of such nature as to oppose the voltage between wiper I8 and center tap I'I as t0 cause the ampliiier IB to so control servomotor I3 as to move the rudder toward zero position. The rate gyro sets up a signal Which opposes the signal derived from the movement of the vane. The value of the signal from the rate gyro depends upon the angular rate of turning of the aircraft. After a corrective rudder has 'been applied, and the airplane moves toward the desired direction of iiight the vane signal decreases which results in a decrease in the amounts of the rudder. The angular rate of turn of the aircraft is dependent upon the amount of rudder, and since the value of the rudder becomes less as the plane moves toward the desired direction, the angular rate is at a maximum as the plane starts to correct for the yaw condition. Therefore as the aircraft initially turns under the rudder resulting from the vane signal the rate gyro signal is at a maximum. It opposes the value of the voltage set up by the vane wiper. The value of the rudder displacement therefore decreases quickly initially. As the aircraft continues to turn under the rudder and tends to head in the direction in which it is moving, the vane moves its wiper I8 toward normal position. Since the value of the rate signal also decreases because the decreased rudder signal reduces the angular rate of turn the rate gyro moves its wiper 49 towards its normal position, The follow up wiper I4 will also be moved by the servomotor toward the normal position on resistor 36. As the vane operated wiper 'I8 under decreasing yaw moves toward the center position on resistor II the follow up wiper I4 also moves toward the center position on resistor 36. The follow up wiper I4 actually is moving in advance of the vane wiper due to the signal derived from the rate gyro. In other words after a corrective rudder has been applied and the turn is initiated, the signal of follow up wiper I4 has less value than the signal obtained from the vane due to the subtractive eilect of the rate gyro on the position of the rudder. As the plane reaches the desired direction of heading, the vane signal is zero. The rate gyro signal will be zero if the craft be not turning -at zero yaw and its wiper 49 will be at the electrical center of resistor 44 consequently the wiper I4 driven by the servomotor will be at the normal position on resistor 36 and the rudder will be centered. If at the time the vane signal was Zero, the aircraft was continuing in a turn or had an angular rate of turn the signal from the rate gyro would effeet operation of the rudder servo to apply oppcsite rudder, to check the tendency of the aircraft to move beyond the desired direction of motion. However, if the aircraft should swing beyond the desired direction of motion, the vane will set up an opposite signal and the rate gyro due to the fact that the aircraft is turning will set up a signal which supplements that of the vane signal instead of setting up a signal which opposes the vane signal in the initial part of the turn. This. effect of the rate gyro is to check any tendency of the aircraft to swing 'beyond the desired direction of motion.

In the aileron channel the directional gyro signal and the vane signal decrease at the same rate so that no control signal is present in the aileron channel. The second operation will be considered when the gyro is headed in one direction butthe aircraitis actually headed and moving.` in a: direction .different from.. thisagyro direction..

Under such condition, the.; directonal'gyro |82 Will move its wiperl'II.y However, sincetheplane isxfmovingiin the direction 1in which itis headed,

theplane will not be in yawedcondition. TheV vane 80.1 therefore will. notdisplace wiper 'I8 of` the rudder controlnetwork or. the Wiper |56; of the :aileron 'controlnetwork The wiper |88 controlledrby the'vaneand .the wiper-'|18 as 'movedJ bythe directional gyro |821Will have a difference oifpotential-.between them which willapply a controlsignal to the aileronamplierV I I6. At

this .timewipers |16and1|80 have `a relative displacement from. the electricalcenters of their resistorszand a .signalisset-up in the aileron control .networkgwhichz isfapplied to. amplifier H6. Suchsignal causes the,.operationror-amplier H 6 to. controljservomotor'H; The servoinotor H3 drivescable*drumY I I and cables.; Hpto position thefailerons in suchmanner as .tov lower the wing. Ofathe. aircraitfonfthe side in which it isdesiredA tofturn in ordertobringi the Vdirection of movement toan accordpwith theidesiredrgyro heading.

ofthe aircraft; Atv this ytime if it is necessary. to turn toitherlef-tzto bringethe direction-of movement.- in line With .the-fdesiredgylO` heading the right aileron wouldfbe.l lowered `and lthe left one would-be raised-.to'tilt theplanefto the left.

Since the-air below. the wingisat somewhat. higher; pressure :than-the. :air above'the wing; the downmovingiright aileron produces considerably more drag than thezupmoving left aileron. The greaterdrag on therightA Wingfwould tend to swing, the plane` tov the right momentarily although it is tilted about the roll axis to the left. With the planevin; such position due to the increased drag of the right WingV the plane would be in` ayawed-conditionz In eiectthe plane would beinasideslipato theyleft: However; the vanev bringv the-plane around so that its direction ofV movement aligns` itself: with; the desired direction' of heading.

When Van'airplane reaches a desired angle of bankl to; elect a-'turnV it isnecessary to move the ailerons-back towardinormal position otherwise the plane. willcontinue `to bank still farther. In order that ,the desiredangle of'bank which the planchas, attained duetothe signal applied from impedance network-.|18 benotrexceeded, an oppositeeontrolfsignal isi-derived to cause the restorationrof the,A ailerons toward neutral position.V Such controlsignal for-restoring the ailerons is. obtainedfromvertical gyro |6|. The vertical giuroA IBI responds-tothel movement of the plane about yits roll-axis which was initiated'from a control signal frorn impedance; network |70; The vertical Agyro4 |6| throughl its operative connection |62 moves wiper |58 of 'impedance network lfwith respect to tsicenter tap ISU. The differenceiof potentialbetweerrwiper |53.;and center tap` |50l arising out of the-movementofjwiper |58 is equal and oppositeto the diierence of potential rising out of the relativey displacements of wipers |16 and. |30 of impedancenetwork |10. ln the.nitialbanking oitheplane when the difference of .potentialbetweenwipers |89 and |15 causes the operation ofamplier. H B and servomotor H3. the servomotor lltthroushfcllowun |'ll positions Willenv` I4 to; set 1 up. between; Wipersv H4 and-|38.aidifferenceof potential equal and opposite, tothat existing-between wipers I8()A and. |75. With` such equal Vand Opposite potentials the network: isbalancedand servomotor I3A is-at rest. When the verticalgyro I3! displaces wiper` |58 withrespect to center tap |60 to set upv adilierence of potential equal and opposite to that betw'eenwipers` |80 and |16, the amplifier I6 is energized to reverse the, direction in which servomotor-||3 originally was operated. This causes the servomotor I3 to lmove wiper I |4 'back to its center'position so'that-no difference of potential between, wipers H4 and leexists. The ailerons being driven, frein-servomctor H3 are therefore in neutral position.;

As the planes direction oi, movement under the actionv or the horizontalcomponent of lift of the banked plane approaches the desired heading the. signal, from thedirectional gyro de creases theretor and @smaller difference of potential existsbetweenwipers and llt which is less than that between Wiper |58 and center tap |60. A differential signal therefore is set up and applied to amplifier-*l |6. This causes the servomotorl H3 toapplygopposite aileron to the aircraftfrom thatv initially` applied. The servomotor thereforeapplies opposite aileron and also throughitsfollow-up means ||`l moves Wiper H4 to balance thecontrol network for the amplilerv channel. The application of opposite aileron tends to decrease thefangle at which the the plane is banked. The vertical gyro lei respends to the decreased angle of bank and therefore moves its wpel` |58 toward its center tap |60. At this time there is an excessive voltage signal. This excess signal is in such direction as to cause amplier Hlt)` restore the ailerons to neutral position andfw-iper H4 to its center position. The action is continuous with decreasing signal inthe directional gyro tending to apply opposite aileron which continues to move the plane toward level flight. The vertical gyro responds to this decreased banking angle and sets up a signalto restore-ailerons to neutral position. The action iscontinuousV so that as the planes direction lof movement assumes the desired direction ofA headingthe individual networks of the control channel for the aileron are in balanced Icondition and the ailerons are in neutral position.

Since an aircraft in a-turn tends to lose altitude it is desirable at this time to apply up elevator in orderto maintaintheoriginal altitude of the aircraft. For this purpose when the plane is in bank position causing the-gym` II toY operate wiper |58y in the aileron channel the vertical gyro |6| also, through. tsyoperative connection 242, movesthe Wipe1j244 ofi-impedance network 25.0 inthe elevatorV contrOl. Channel. The movement given to wiper/2.44. from operative connection 242 is such astoapply up elevator irrespective of theV direction in which the plane moves about the roll axis. The operation of the elevator network,yamplier 2|6., and servomotor 2|3 is the same asV the other channels, and the up elevatorderived frommovement ofwiper 244 anticipates any, loss of elevation that the plane might undergo and maintains the plane at the desired altitude. As the `plane assumes level flight the wiper 244 .moves toward. normal position reversing the ,movement of the elevators whereby the elevators arealso restored to normal position. andthe elevator networks are in .normal hosition,

Figure 2 The new principle of controlling an aircraft in night by controlling the rudder from a yaw sensing devicek and the roll axis control surfaces by the coaction of the yaw sensing device and the directional gyro has been embodied in a modiflcation illustrated in Figure lThe apparatus of Figure 2 is adapted to control the night of a tailless airplane, often referred to as the Flying Wing. As is presently known, the Flying Wing has tWo sets of control. surfaces. Both sets of control surfaces are mounted in the trailing edges of the left and right wings. The outboard control surface in each wing is termed the rudder and controls the movement of the Fly-- ing Wing about the turn axis. The inboard control surface in each wing comprises a set of control surfaces whose function is to control the movement of the aircraft about the roll axis and also about the pitch axis. For this purpose the control surfaces may be moved together in one direction to act as the conventional elevators. On`other occasions, they may be made to move in opposite directions in the same manner as the conventional ailerons. The term elevons has been applied to the inboard control surfaces since they are in the nature of elevators and also ailerons. The rudder in each wing instead of moving about the vertical axis moves about a horizontal axis, and its purpose is to increase the drag of its wing when it is moved to open position and to decrease its drag when moved to closed position.

Referring to Figure 2, the rudder, not shown, in the right wing is operated by cables 424 extending from a cable drum 42.5. The cable drum 4251s driven from a servomotor 428. The servomotor 429 may be of thetype disclosed in my application Ser. No. 447,989, mentioned above. The rudder in the left wing is operated by cables '4|0' extending from the cable drum fill. The cable drum 4|| is driven by a servomotor 4I2 which is similar to servomotor 42E. As disclosed in that prior application, Veach servo-motor' includestwo operating solenoids. Servomotor 4|2 has an operating solenoid M9 connected at one end through leads 4|8, 439 to a switch terminal 439. The opposite end of ksolenoid H3 is connected through lead 425Mo a switch contact 45.9.

The other operating solenoid 414 of servomotor y4|2 has one end connected through leads 431, 434 to a switch terminal The opposite end of solenoid 444 is connected through lead 4| 9 to a switch contact 452. The servomotor 423 has an operating solenoid 454| connected through leads 435. and 498 to switch terminal 439. The opposite end of solenoid Si is connected through lead 433 to switch contact 499. Operating solenoid 439 of servomotor 428 has one end connected through leads 432 and 434 to switch terminal 438. rllhe opposite end of solenoid 439 is connected through lead 435 to a switch contact 459.

Switch terminals 439 489 are housed within an amplifier 448. Terminal 438 forms a portion of a switch whose arm may be actuated from an electromagnetic relay 4414. The arm of the switch is of the spring loaded type. As shown, this arm has its mounting terminal connected to one side of al battery whose opposite end is connected to ground. rferminal 438 forms a portion of a switch whose arm may be operated by an -electromagnetic relay 44,3. The switch arm is spring loaded. As shown, the switch arm is connected to one side of a battery, the opposite side of the battery being connectedto ground. The amplifier 440 may be of the type disclosed in application Ser. No. 447,989 dated June 22, 1942. This amplifier 440 has a signal input terminal 442 and a ground terminal 44|. The amplifier is supplied from a source of load current 508 which may be an inverter (not shown). As disclosed in the prior application, the operation of relay 443 or 444 depends upon the phase relationship between the input signal applied between terminals 442 and 44| and the supply voltage derived from source 500. For purposes of explanation, we may consider that relay 448 is operated-when it is desired to yaw the aircraft to the left and relay 444 is operated when it is desired to yaw the aircraft to the right.

The control signal to amplifier 448 is derived from a balanceable network 488; the input terminals of the amplifier being connected on a circuit extending from input terminal 442, lead 41|, impedance network 480, ground 414, and to the grounded terminal 44| of the amplifier. Im- -pedance network 480 comprises a resistor 48| whose opposite ends are connected through respective resistors 482 and 483 to a secondary 484 of a transformer 485. The primary 499 of the transformer 485 is connected to a suitable source of alternating voltages 508. Since the apparatus of Figure 2 has several secondary windings which may have a common primary winding, the primary winding of the transformer is indicated in each instance by the reference character 499. A Wiper 491 may be positioned over the surface of resistor 48|. It may be seen that a potentiometer circuit is therefore formed from the left end of the secondary 484 through resistor resistor 48|, and resistor 482 to the opposite end of secondary 484. A parallel circuit extends from the left end of secondary 484 through lead 481, a resistor 488, lead 489, a resistor 49|, and lead 492 to the opposite end of secondary 484. A wiper 493 may be positioned along the surface of resistor 488 and a wiper 494 may be positioned along the surface of resistor 49|. A resistor 495 is connected between the wipers 493 and 494. The resistor 495 has a center tap 495i.

The two parallel circuits connected to the ends of secondary 484 form a bridge arrangement. The output of this bridge is measured across center tap 496 and wiper 491. In normal position the wipers 493 and 494 are in their inward position, as shown, and wiper 491 is at the electrical center of its resistor 48| When thus positioned, the potential of wiper 491 is the same as that of the center tap 496. If wiper 491 be positioned to either side of the electrical center of resistor 43|, a difference of potential between the center tap 499 and wiper 491 exists. Center tap 49S is connected through lead 41! to the input terminal 442. Wiper 491 is connected to ground 414. It is therefore apparent that any difference of potential existing between center tap 496 and wiper 491 is applied to amplifier 440.

Wiper 491 is positioned through an operative connection 498 by a vane l499. The vane 499 be of the type disclosed in Patent 1,119,324, dated December 1, 1914. In that patent, the vane may receive its motion from the movement of the air with respect to the heading of the aircraft. rlhis vane may be adapted to affect the movement of operative connection 498.

The servomotors 4| 2 and 428, which have their respective operating solenoids 4| 3, 4i4 and 43D, 43| controlled from relays 443 and 444, are also controlled through a series of relay contacts comprising/ aleft outer pai1g450; 451; a left inner. set 452,453, 454;;a1right-,inner'set455, 456, 450; and a rightouter pairv 4,58, 459. Alead 412V extends from inner contact 45| ofil thev leftrouter pair to left contact .455 of theright inner set. A lead 413 extends from right contact 454 of the left inner set to inner contact. y458.0f-the right outer pair. Contact 453, which. is. positioned between contacts 452and 45.4,is-connected to ground. Contact 456, which ispositionedbetween contacts 455 and 459, isconnectedto ground. Contacts 455 and 45|'y constitute alimit switch. `This limit Switch is spring biased so that contacts 450, 45| engageeach other, as shown. A depending portion of contact 450 may be engaged to separate the contacts. Contacts 452- and 453 are spring biased so as to contact one another, but ets-shown, a depending portion. of contact 453 may be en gaged to separate contacts 452 and 453 and to engage contacts453 and 454. Similarly, middle contact 455 is spring biased to engage contact 459, but as shownfcontact 45B has a depending portion which may befengaged to separate contacts 456 and 4S0'andfto1engage contact455 with contact 455; Contacts 458 and 459- constitute a limit switch. Contact 459 isv normally spring biased to engage contact 458, asf shown. Contact 459 has a depending portion which may be engaged to separate contactsn458and` 459. The depending portion of contact 450l and contact 453 are actuated by a member 451 to which wiper 493A is secured. The member'45l is driven through a follow up connection from cable drum 411 of servomotor 412. The depending portions of contacts 455and' 459;are operated by a member 452 to which wiper 494'is attached. The member 452 is operated through a follow up connection 464 from cable drum '425' of servomotor 425.

With` the arrangement of the'members 451 and 452 as shown, the rudder in each wing is at closed position. If relay 443in amplifier 440 closes its switch indicating that a turn tothe left is desired, a circuit is completed at one endi for operating solenoid 413 throughleads 435 and 41S from terminal 439 and for operating solenoid 43| through leads 438 and 435Y from terminal 435. The circuit extending from the opposite end of solenoid 431, is open between contacts455 and 450. However, the circuit from theA opposite end of operating solenoid 413 is -completed through lead 420', the left outer pairof'contactsf450, 451 and left and middle contacts-455, 455lof the right inner set to ground. The servomotor 412 isthus controlled by itsk operating solenoid 4 I 3 and drives its rudder toward open position;

Suppose that theleft rudder'assumes a partiallyl open position dueto the .operation of operating coil 413. At this time, member 451 has been moved slightly' to theleft through its operative connection 453 from cable drum 41|. Contacts 452- and 453 ofv thef. left vinner Vset will therefore be closed, but vcontacts 453 and .454 will be separated.

Assume atthisitimewhile the aircraft is moving about itsv turn-axis undercontrol of the rudder that it is desired to stop the aircraft from turning. Such elimination of ,turning may be effected by opening the right -rudder to a greater extent than Ythat of'the rudder inthe left wing. However, it is desirable that the plane iiy at all times with as low resistanceto iiightasit is possible to obtain. The:eliminationlofturning may also be,` obtained lby; decreasingY theresistance on theY leftwing. Atjthisltimefrelay 444which produces an; effectppositefto i thatzof previouslyl operated.

relay 443 would be `operated to straighten the plane out. Operation of relay 444 closes the circuits for operating solenoidsV 4530" and1 41'4, up to one end of 'the solenoids; Operating solenoi'd'43'0 tends to open the right rudder whereas solenoid 414, when operated, causes theA closing off the left rudder. At this time the left rudder is, asstatei in a partially open position. The circuit through the opposite end'of operating solenoid 430e'xtend's from lead 435, contacts 459, 458; lead'413, to coni-'- tact 454 where'it is broken; The circuit from the opposite end of roperating solenoid 414 extends through lead 419, contact 452, and', due to the fact that member 451 has been movedto the` left; through contact 453 and to ground. The operating solenoid 414 is therefore energizedto cause the closing of the'left rudder permitting the, plane to straighten out or to stop turning. As the left rudder moves toward' closed positigi, the follow up connection 453 moves the member 451`to separate contacts 452 and453, deenergizingV solenoid 4 I4, and thereby stopsservomotor 412. A similar operation occurs when the'right rudder is moved toward open position in that contacts 456; '4150 are closed as member 462` moves to the right thereby partially closing the circuit through solenoid 431, to permit closing the right rudder whenrelay 443 is energized. If the aircraft'is to change Vfrornla left turning action to a'right turning actionitis apparent from' above that the left'rudderjcloses before the right rudder opens;

It may be seen, therefore,v that through trie arrangement of the relay contacts described above, only one rudderv may be placed in operated condition at'one time and that due to this'opera.- tion the drag on the wing is'kept to a minimum;

It may be at .times desirable vto carry a'rudder in a partially operated position. Such al condition might arise due to unsymmetricalpower in the aircraft. An arrangement has been provided whereby the rudder may be continually maine tained in a partially operated position. For this purpose, a wiper501, havingV a lead 502 may be adjusted over the surface of resistor 483 to shunt any desired portion of the resistor. Similarly,a wiper 503 having a lead 504 may' be positioned along resistor 482 to shunt any portion thereof'. The wipers 501 and 503 are operated from a coin.- mon shaft 505 which moves-wipers 501 and 503 Iin opposite directions so that if the wiper 501-` is moved to shunt a greater portionof resistor 483| the wiper 503 will be positioned toshunt a lesser portionof'resistor 482. It has been stated that normally wiper 491 and center tap 495Y are at .the

samepotential with thewipers 50| and 503 .inthev position as shown. If wiper 501 be moved' to shunt a-greater portion of Iresistor 483, .the potentialof wiper 491 will more nearlyV approachthe potential of the-left end ofsecondary 484 than exists in the Aposition shown.v The potential of. center tap 495 will not change by operation of wipers 501, 503-.A Therefore, a diierence of potential between wiper 491 and center tap 496 exists which will cause the amplifier 440 to operate one of its relays, which in turn causes the servomotor to position the rudder in partially operated. position. The operatingservomotor will position its followY up member to alter thepotential ofthe center tap 496- until. it isequaltothat of wiper 491.A When thev potential of center tap 49E/and wiper'491 is thesame, the-ampliner-MD no longer operates and the rudderremains in the partiallyy operated posi-,-

tion;Y The extent to .which.thelrudderisioperated; depends'` upon theamount ofimbalance of the* network.

The elevons, which are not shown, control the movement of the aircraft about the pitch and roll axes. The elevon in the right wing is operated from cables 100 extending from cable drum 109 driven by servomotor 101. Servomotor 101 is similar to servomotor |126. The servomotor 101 is controlled from an amplifier 104. The amplifier 104 is similar to amplifier 440. The elevon in the left wing is operated by cables 102 extending from a cable drum 123. Cable drum 123 is driven from servornotor 103. Servornotor 103 may be similar to servomotor I. Servomotor 103 is controlled by an amplifier 126. The ainpliiier 126 may be similar to the amplier 104. The ampliers 10d and 126 may be operated to so control their servomotors as to effect the movement of the elevons in either the same direction to give elevator action or in opposite directions to produce aileron action. The amplifier 104 has an input terminal 105 and a ground terminal 106. its supply leads are connected to source 500. Amplifier 16d is controlled by a plurality of networks 116, 130 and 160. To effect the operation of ampliiier 194 so as to produce elevator operation of the right elevon, a signal may be applied to amplier 19d through a circuit extending from lead 195, impedance network 110, leads 120 and 120a, the right hand portion of a resistor 121, lead 124, impedance network 130, ground 140, and to the grounded terminal 106 of ampliler 104. The amplier 126 has an input terminal 101 and a ground terminal 108. The power terminals of amplifier are connected to supply Amplifier is controlled by network 130 and two further networks 140 and 110. A signal for operating ampliiier 126 to eiiect the operation of the left elevon as an elevator is derived from a circuit extending from input 101, impedance network 110, leads 100 and 1806i, the left-hand portion of resistor 121, leave ld, impedance network 166, to ground 1256, and` to the grounded terminal 108 of ampliiier 126.

The impedance network 110 in the input circuit of amplifier 104 is in the form of a Wheatstone bridge. Two legs of this bridge are formed by a resistor 111 having its opposite ends connected through leads 112 and 113 to the respective ends of a secondary 114 of a transformer 115. The transformer 115 has a primary 490. A manually operable wiper 116 may be positioned over the n The other two legs of the surface of resistor 111. bridge are formed by a resistor 118 which has its opposite ends connected to the respective ends of secondary 110 through leads 112 and 113. A wiper 119 may be positioned over the surface of resistor 118. The wiper 119 may be moved through a follow up connection 111 extending to cable drum 109. The wiper 119 is connected to lead 105 which is the input to ampliiier 104.

In normal position the wipers 116 and 119 are at the electrical centers of their respective resistors '111 and 118. When in such position the wipers 116 and 116 are at the same potential. If wiper 116 be manually moved from its electrical center, its potential with respect to wiper 119 will be altered. In order that the wipers 116 and 'H9 may be at the same potential, it will be necessary, therefor, for servomotor 10| to adjust wiper 116 accordingly. Since wiper 119 can only be moved with a concurrent movement to the right elevon, it may be seen that wiper 116 may be adjusted to alter the position of the right elevon in order that no potential diiierence exists between wipers 116 and 119. Wiper 116 and its resistor 111 are termed the centering means of -1 a follow up connection 12H9 from cable drum 18 the right elevon since they are used to adjust its position until it normally reaches center position.

Wiper 116 is connected through a lead 120 t0 one end of the resistor '121. Resistor 121 has a center tap 122 which is connected through the lead 125i' to a wiper 138 of the impedance network 130. Impedance network '139 is in the form of a 'vheatstone bridge. To legs of this bridge are formed by a resistor 131 having its opposite ends connected through leads 132 and 133 to the respective ends of a secondary 134 of a transformer '135. The transformer 135 has a primary winding 95. A manually adjustable wiper 136 may be positioned along the surface of resistor 13 The iper 136 is connected to ground140. The other two legs of the bridge are formed by a resistor 151 whose opposite ends are connected through leads 132 and 133 to the respective ends of secondary itt. A wiper 163 may he positioned over the surface of resistor The wiper 13S receives its movement from an operative connection 139 extending from a vertical gyro ri'he vertical gyro 125 may be of the type disclosed in my application previously referred to, Ser No. 447,989. Movement ofthe aircraft about its pitch axis causes the vertical gyro 125 to apply motion to the operative connection '139 and to wiper 138.

Zihe impedance network r/ portion of the input circuit to anipiinci the forni of a Wheatstoiie bridge. Two legs of this bridge are formed by a resistor iii whose opposite ends are connected through leads and 113 to the respective ends of secondary oi a transformer The transformer iii has a primary winding The resistor 'nas a wiper V56 which may be manually moved over its surface. Wiper 116 is connected through a lead 66 to one end of resistor W1.

The other two legs of the bridge are formed by a resistor 111 whose opposite ends are connected through leads 1;'2 and 'ile to the respective ends of secondary winding A wiper 116 may be positioned over the surface oi resistor 111. The wiper 118 receives its motion through Wiper is connected to the input l0? oi' ainplirer 26 Wiper i'i and its resistor constitute a centering means for the left elevon s' impedance networks 'V36 and are similarly related to their amplifiers and servcinotors.

in addition to the means for centering the elevons individually, means is also provided to move them in the same direction si`I 1y. Such means is provided in ord-.ei e a slight `amount ci up elevon may be carrie each wing or ii necessary a slight amount oi down elevon may be carried. Such means :Ter concomitantly adjusting both elevons in Vded in the impedance network i which is c .on to the input circuits of amplifiers idf normal position, the wipers 'H6 and network 116 are at the electrical centers or their respective resistors r11 and Similarly, wipers 1&9 and 'H6 of network iid are the electrical centers of their respective resistors il@ and 1H. Wipers 13E and oi netwerk. i3 also at the electrical centers oi their resistors 131 and 13i. Wipers and Yz with respect to its electrical center, di er of potential exists between wipers and Wiper 136 is connected to a coninion ground for ampliiiers 104 and 126. Wiper 136, on 'the other hand, is connected to amplifier Edil through lead 120, impedance network 116, input lead 19 loa.v Similarly, wiper 'i3d is -connected through lead "85, and impedance network Titi, to inputv lead 'lill of amplifier tt. Wipers 738, il?, TES on the one hand andy wipers 138, llt and ils on the other hand are at the same potential. The difference of potential which at this time exists between wiper 'i3d and wiper '538 will therefore exist between input terminal E of amplifier tot and the grounded terminal liit of amplifier it.

This same dierence oi potential will also exist between input terminal 'itl of amplifier 'lit and grounded terminal it oi amplifier H6. The amplifiers lee and 'EES will therefore control their respective servomotors 'icl and 'itt to move their elevons in the same direction. rlhe movement oi the servomotors to position the elevons will also operate through follow up means 'i il and 'lle to set up equal and opposing voltages to thateiiist ing between wipers 'itt and it.4 When such voltage is set up by the follow up means on their respective impedance networks il@ and lill, the amplifiers ille and lit no longer operate. The elevonsv have thus been moved to a position which has been determined by the movement of the manually operable wiper its. The amount oi adjustment given to wiper les may be varied with conditions. rheabove description relates to' the operation of the elevons as elevators, in which operation both elevons were moved together in the same direction.

A network has been devised for obtaining the operation or" the elevons as ailerons. The elevons when operated as ailerons may be said to be dinerentially moved. Such differential movement of the elevons may be secured by applying voltage of one phase to one amplifier and by applying a voltage of the opposite phase concomitantly to the opposite or the other amplifier. The diierential effect may be said to be secured by this differential signal. The difierential signal is derived from voltage drops along the resistor il which has its opposite ends connected to leads 78de, ldt'. of the input circuits of amplifiers lt, EES. As previously explained, resistor l2! has a center tap 'E22 which is connected through impedance network 'ist to ground ist. Consequently, in normal position, as shown, the center tap "i22 is at the same potential as ground lot of ampliner 'it and ground 708 of amplier 'ld If current passes through resistor l2! during a given half cycle from the left end toward the right end, the left end of resistor l2! is at a higher potential than the right end during that half cycle. The left end of resistor 'sii is connected through lead 'itt and impedance network 'Vit to input terminal lill of amplier l. The right end oi resistor l2! is connected through lead l2@ through network ll to input 'HB5 of amplifier ldd. The left end of resistor 12| has as great a potential above that of center tap 122 as the right end of resistor l2! is below the potential of center tap 122. In other words, the potentials of the left' and right end of resistor '52S with respect to the center tap are equal but of opposite phase. The opposite phase of the potentials may be termed a differential signal. The potential at the left end o resistor 72| is therefore applied to amplifier 725 and an equal but opposite potential is applied to input '105 of amplifier 104. These signals cause the operation of amplifiers lof: and 126. The ampliers, when operated, cause their servomotors lill and 'm3 to move their respective elevons in opposite directions. This opposite movement of the elevons is similar to the movement applied tothe conventional ailerons.

Y The current through resistor 'ii is derived from a series of connected networksv ist and itil through' a circuit extending from the lett end of resistor l2i, impedance network lilo, lead lle, and impedance network lt to the right end of resistor lZl..

The impedance networki is in the form oi a Wheatstone bridge. rwo legs of this bridge are formed by a resistor 'mi whose opposite ends are connected through leads i122 and 'dit to the respective ends of a secondary winding Mil oi a transformer M5.- 'lihe transformer li has a primary winding dell. A wiper 'MS may be moved over the surface of resistor list. The wiper is moved from vane lieg through an o erativeconnection 'Eril'. The oppositel two legs of the bridge are formed by a resistor '48 whose opposite ends are connected through leads 'it and H53 to? the respective ends of secondary winding leid. IThe wiper 'idd may be moved over the surface oi resister itt. The wiper i139 receives its motion through an operative connection l from a directional gyro tt. Directional gyro '55 may be of the type disclosed in my application Ser. No', 447,989, referred to above, In normal position, wipers iet and 'ille are at the electrical centers of their respective resistors 'itl and In such position wipers it@ and la are at the same potential.v Wiper 'itt is` connected through. lead' illd to the left end of resistor li. wiper it is connected through lead lli? to wiper it of an impedance network '565'. Y

Impedance network is in the form of a Wheatstene bridge. Two legs ot thisl bridge are formed by a resistor 'itii whose opposite ends are connected through leads 'it-i2- and '153- to the opposite ends of a secondary winding le@ of a transformer lt. The transformer 1&5 has a primary winding fitti. A wiper 'ii may be manu-ally moved over the surface of resistor ll. A connection litio extends from wiper 'ltd to the right end of resistor 'i2-i. The other two legs of the bridge: are formed by a resistor ll whose opposite endsI are connected through leads it and 'E53 to the respective ends of secondary winding '15s; lhe wiper 163 which may be adjusted over the surface of resistor 'itl derives its motion through a mechanical connection '59 from vertical gyro '$25. Movement of the aircraft about its roll axis causes the vertical gyro to apply movement to the operative connection ld and thereby position wiper its.

YIn normal position as previously stated, the wipers ist and 'm9 of impedance network Mt are at the electrical centers of their' respective resistors 'Mi and i138. When so positioned, the wipers llti and 'MS- are at the same potential. Similarly, in normal. position, wipers 'E65 and T68 are at the electrical centers oi their respective resistorsv 'i'' and itl. In normal position, wipers ist and itc are at the same potential. If wipe 'itt is manually adjusted with respect to its electrical cen-ter a potential difference exists between wipers 16:5 and '558. Wipers 'it and 'sito are at the same potential, and wiper 'it is therefore also at the potential of wiper M9. A difference of potenti-al therefore exists between wiper T66 and wiper 'lila This difference of potential causes a current to pass through vresistor i. The potential at center tap '522 is the mean oi the potential between Wipers and le?. Center tap T22 is connected through network i5@ to ground. The potential on 'MQ is applied to amplier 25 through network llt. The potential of wiper 'Kt is applied through network 'i553 to ampliiier fi.. rEhe potentials applied to amplii rs 'H34 and it with respect to the center tap '22 are of equal but opposite phase. A differential signal is thereby applied to each ampliner causing the ampliiiers lii and to effect the operation of their servomotors 'iti and tot in opposite directions. The operation or" the servo-motors causes opposite movements oi the elevons. The servoinotors in turn operate their follow up connections lil and 'its to set up a voltage on networks llil and 'Vit equal and opposite to that existing between their amplifier inputs and center tap '622 which is the same as ground potential. 'The Wiper itt may therefore he manually operated to alter in reverse direction the position or the ailerons.

Reverting to the vane to, it is proposed to pro vide the vane with damping means whereby the vane will not r Aspend to temporary or local gusts of air Fout will respond to prolonged yav.-v cono;- tions. ln Figure 3, the vane 2Q is supported on a shaft rThe shaft iil extends vertically through a part oi the aircrafts traine to2, and a collar on shalt niay rest on the traine and serve to rotatably support the shaft. The shaft Sil@ which drives the wipers i8, 58?, Figure l, at its lower end has affixed thereto a yoke eilt. ends of the yoke are journaled to receive trunnions of a Carden ring Sti. The Carden ring i n turn is journaled to receive the of a rotor Stil, The rotor @39 may be rotate ley any conventional ineans, such as an electric motor or by air operated means, not shown. Centering springs si! and Si? extend from the cardan ring on opposite sid-es of trunnion to a common point on the yolre 234.

rotation of shaft is resisted by the rotor which processes about the axis of trunnions and 8%. rlhis rotation about the axis of ti nions ttt; is resisted by either oenteri a springs dii and Sill depending upon the direc of rotation about said axis. By such operai the torque applied to the vane due to local gusts is absorbed by the action of the rotor i339 in rotating about the axis o trunnions When the torque applied to the vane Si? is prolonged in nature, the rotor Bilt will process about the axis or" trunnions Ste until such time as the tension on either spring 8H or SEZ supplies a torque equal to that tending to process the eyro rotor At this time the rotor E@ will have reached its maximum amount of procession. rChe vane Sil will now under the effect of the torque applied hy the prolonged condition of yavv tend to rotate shaft St! and to position wipers i8 and 58o of Figure l. rihe vane 8d vill therefore respond only to prolonged conditions of yaW and will not oscillate dus to local gusts which are encountered by the aircraft.

Operation The operation of the apparatus in ence between them although they have been moved with respect to the electrical centers of their respective resistors, and since sliders and iii-G of network l@ are ooth in their center positions, no current Will therefore new through resistor 12E. No signal will at this tir. e be ap'A plied to ampliiiers lofi and 'iifl to diiierentially adjust the elevons.

However, the increment of vane through its operative connection displaces wiper al of the rudder networks with respect to the electrical center or" resistor li. Suppose Wiper 59'! is moved toward the right of the center ot resistor 553i. Consider in a given half cycle the right end of secondary los is negative with respect to the left end. Wiper is electrically wiper de? and center t A.c o.' potential causes the air l to hec erative to close electro; a e c ri. rihe operation or" the relay fifi turn closes a circuit through servornotor operating solei c...d causing the servoznotor to drive its rudder toward open position. The servoinotor drives its follow up to position a inernloer to the right to nia-he the potential ot center tap the saine that t wiper till. the potentials are equal the Oi relay uit is rie-energized. The plane responds to the effect or" the rudder and begins to move in a turn so that it tends to head h1 the direction in which the plane is moving.

Such a change ci heading of aircraft changes the amount of the signal iroin vane since the vane is positioned in ac ordance with the direction of the relative air. Since the vane signal decreases, the Wiper is moved letivard toward the electrical center of its resistor The repositioning oi Wiper till' leaves an unhalance voltage in network ist dus to the posi-ion assumed by the member failli driven 'oy the follow up from the operated servoinotor. The amplifier therefore calls for reverse rotation of the se'vomotor. The servornotor responds to the reverse signal and moves the right rudder toa/'ard closed position and again operates its follow up to s up an equal potential on center tap f i? Which is present on Wiper The action is con tinuous; the vane to the det t e yavf angle and continues to move its -f toward the electrical enter of resistor sti and the amplifier causes the servoinotor to drive the rudder further toward closed position and to balance network At the 1e that the piane is headed in the desired direction of movement, the vane is in its n= rinal position, the nei-avori: .S is bala. ced, and l. is in closed position. Since the va;A `l and the deviation signal in the network ease at rate as yavv is rerrove have no difierential movement and no operation of the eievons taires place.

The opera n will he considered when the plane is headed and moving in tion but is not moving in desire-i direction indicated 'oy the directional the directional gyro im will inove its since the piane is not rection. The vane ist responds to the reative air and since there is no yaw it does not inove its Wiper MG in the elevolcontrol. ilhen the directional gyro moved its wiper E at this time in accordance .r ith the deviation sigv nal, wiper 'i156 is at the electrical center of resister lili. l

et at el. :viper hea-Lied in the d di- Wipers 'it and me have a difference aecavos of potential which is now applied across resistor This signal as applied across resistor i sets up a differential signal in the amplifiers and ltd which effects. aileron operation oi tl e elevons. The positioning of the elevons also causes the operation of the follow up mechanisms lll and 'i219 which set up a signal equal but opposed to the initiating signal.

it is apparent that the magnitude of the bank is proportional to the magnitude ci the deviation between the gyro indication of the craft and its direction or movement which at this time is the same as its heading. While it is desirable that the banl of the plane be proportional to the magnitude or" the deviation, the baril; of the plane should not be oi" greater magnitude than the baril-z resulting from the deviation signal. When a plane is placed in a banked position, it necessary to decrease the amount of aileron if a desired bank is to be maintained; it will continue in this banked position even though the aileron or elevons are returned to central posiion. The magnitude ci the bank which is proportional to the deviation signal is therefore maintained through the operation of the vertical gyro The vertical gyro lii responds to the movement of the plane into the banked position and moves its operative connection ite to adjust Wiper 'it With respect to the electric center of resistor ll. The signal between Wipers E63 and itt resulting from the movement of wiper 'il by the v rtical gyro 12e sets up a signal on ampliers 'itis and itt which is opposite to the signal arising out of the difference of potential between wipers it and i, The amplifiers and '52E are thereby operated to cause the servoinotors lili and itil to drive the elevons toward center position. The plane is now an angle of bank which it maintains and which it does not exceed. The banked plane now turns so that its direction of movement assumes the desired gyro indicated direction. .es the planes direction oi movement which is the direction of heading now approaches the desired gyro direction of movement, the signal from directional gjro decreases. rihe Wiper Trie is therefore moved toward the electrical center of wiper hit. The difference of potential between Wiper and wiper is opposed to the difierence of potential. between Wipers its and it. These voltages are in opposition; and there being a difference of voltage, a voltage drop exists across resistor isi. This voltage drop is in the opposite direction from that originally resulting from the initial displacement of Wiper hie from the directional gyro. The amplifiers loll and 'it respond to this opposite diierential signal and apply opposite aileron. The follow up members 'iii' l'i again set up equal and opposing signals. The craft responds to the opposite aileron and decreases its angle of bank. in View of the decreased angle oi bank, the vertical gyro 25 reverses the motion applied to its operative connection ist and moves wiper 76E toward the electrical center or resistor it?. The signa-l resulting from the motion of the vertical gyro "E25 causes the servomotors to restore their ailerons toward central position. The action is continuous; the directional gyro signal continues to decrease to eiiect the application oi opposite aileron and the vertical gyro responds to the decreased bank and tends to restore the elevons to center position. At the time the planes heading and direction of movement coincide with ther desired gyro heading, the .Wiper 749 is at the electrical center or resistor '55S and the wiper 'i is at the electrical center of resistor it?. During this turning movement of the the vane functions to cause operation oi the rudder to remove any yaw which the plane may have While in such turn. The networks are ultimately individually balanced, the elevons are in center position.

The vertical gyro i also functions to stabilize the craft about its roll asis. if the plane be headed in the des d direction be movi; g in the desired direction, the plane may, due to external causes, assume a banked position. The plane is automatically brought ba to level position by the operation of vertical gyro The gyro responds to movement of the piane about its roll axis and adjusts Wiper The movement of Wiper it sets up a diierence oi potential between i per and wiper '553. difference or" poten l results curent ilovving through resistor is current through the resistor /i the differential action ci the elevons from their respective servoinotors. The servoinotors also operate their follow ups i i l and il@ to set up equal but opposing voltages. The plane responds to the operated elevons and moves toward level i'ligi t. is the piane moves toward level night, the vertical eyro E25 responds to this smaller angle ci bank. The gyro i725 consequently rnoves wiper toward the electrical center of resistor ./-i reverse signal is therefore set up in the ampli-lors 'led and 525 which causes them to lmove their elevcns toward normal position. The action is continuous.

rThe plane is also stabilized with respect to movement thereof about the pitch axis. Such ettveen W iper the displaced Wiper and Wiper 73S is connected to ground grounded terminals 'i3d and 23 oi amplifiers and itil. The potential of Wiper 'E313 is applied through lead l', impedance network liti, through input lead to amplifier 'its on the one hand and through lead network llt to input terminal of amp-lirici' itt on the other hand. The ampi lors l'i and lli-i3 therefore receive a voltage of li e phase with respect to their ground connections. The ainpliers i'ifi and 'i255 effect the operation of their servornotors 'lili 183. The servomotors operate their respective elevons in the same direction. Servoriotor 'iti drives follow up lil to position wiper riti to set up between wiper "5!9 and wiper lis a voltage equal but opposed to that existing between Wiper 738 and wiper i. Similarly, servomotor 'EES through follow up Tit positions wiper llc to set up a voltage between wiper and wiper llt equal but opposed to the voltage between WiperY `the electrical center of resistor '31'. A smaller difference of potential therefore exists betr-.reen wipers 138 and 73S than existed initially. This potential between Wipers i353 and E35 is at this time less than the potential het*v 1een wiper lle and H5 on the one hand and Wipers 'l's' on the other hand. rEllis unbalance voltage causes the amplifiers lis-3 and lifl to operate. The amplifiers and 't28 cause their servou motors tilt to move in an opposite rection from that initially given to them. The control surfaces are therefore moved toward center position. The action is continuous, being of such character that as the level position the vertical gyro has moved wiper to the electrical center of res.4 or T53? and the servoinotors lcd and '.1225 have ed their follow up Wipers lli.' and llt to the electrical enters of resistors 'Ht and lll. At this time the inoividual networks are balanced condition and the elevons are in normal position.

It is now apparent that we have embodied apparatus novel principle of automatically Acontrolling an aircraft in night. The embodiments described eliminate unnecessary operation of the ailerons of the aircraft by only operating the rudder when iu is desired merely streamline the craft or to cause the aircraft to head in a desired direction of movement. The f n of turning the craft to change the direction of movement as distingui ned froin change in headn ing is effected ley operation oi the ailerons. This elimination of the u .necessary opera-tion of the ailerons dispenses with unnecessar,7 of the plane. lt is also e ident that We have devise;`l ap paratus includes a novel circuit angenient for the control of the elevons in cir function both as ailerons and also as elevators.

l claim:

l. Flight control apparatus for an aircraft SCE to the of movement of said aircraft, control ...ins responsive to the change of heading of said operating means for control surmeans including coth said control means for controlling one operating ea-ns, and rneans including said change of heading responsive means for controlling another operating means. iight control apparatus for aircraft having two control surfaces, said apparatus cornprising: control respon 've to the change of heading said aircraft with respect to the direction or movement of said aircraft, control means responsive to the change of heading of said, aircraft, operating ineens for said control surfaces, ineens including both of control inea-ns for controlling one operating means, and i-.eans including said change of heading respon sive means for controlling another operating vns, s; d control means eecting concurrent .ration of said operating means. i A flight control apparatus for airhaving one control surface for controlling the movement of said aircraft aoout one axis, another control surface for controlling the movenient of d aircraft an axis perpendicust apparatus comprising:

t control ineans responsive to the change of seid aircraft "lith respect to the of movement, a second control ineens ren naive to the change of heading of said aircraft, operating means for said control surfaces,

Uit

cha-nge of heading of said aircraft, a third coni.

and

con-

con-

means includi third control means for trolling the operating means for the second trol surface.

5. night control apparatus for an Acraft having three control surfaces, apparatus comprising: a first control means esponsive to the difference between the headinft of lsaid aircraft and the direction of increment of said aircraft, a second control rneans responsive to i"ne change of heading of aircraft, a third control nieans responsive to the move-; ent of said aircraft about an axis perpendicular' to tl e direction of movement, operating ineens for control surfaces, means including the inst conu trol .neans for controlli -g the operating means for the first control surface, means including said first and second control means for controlling the operating means for the second control surface, and means including the third control inea-ns for controlling the operating means for the third control surface.

G. i-i flight control apparatus for an aircraft having three controi surfaces, each control surface controlling the movement of the aircraft about one of three respectively perpendicular said apparatus comprising: a nrst control means responsive to the difference between the eading of said aircraft and the direction of movement of said aircraft, a second control means responsive to the change of head e of said a third control ineans rospo e -to the movement of said aircr it about perpendicular to the direction of movement of said airoperating means for control surfaces, mea-ns associating the Lrst control means with the operating means of the first control surface, ineens associating said first and second control means with the operating mea. s for the second control surface, and ineans including said third control means for controlling operati..-g means for the third control surface.

7. A flight control apparatus for craft having three control surfaces, each controling the movement of the aircraft one of lree respectivelgr perpendicular axes, said ape .-ratus comprising: a nrst control ineans responsive to the difference between the heading of said aircraft and the relative direction movement of the aircraft air, second con trol means responsive to the change of heading of said aircraft. a third control means responsive to the movement of said aircraft about an axis which movement is perpendicular to the direction of heading of aircraft, g means for control surfaces, inclue. the first control ineens for controlling the operating means of the first control surface, inea-ns associating said rst and second control means with the operating ineens of the second control surface to cause said aircraft to move about the axis an air- 2? is'pcrpendicular to the direction ,"ng of said aircraft, and means including control means for cont 'olling the operating means for the third control surface.

s. Motor control means comprising, an irnpedance network having an adjustable element, a connection from element to one end of an impedance element, a connection from the other end of the impedance element to said network, a motor, a motor controller, a connection from one end of the impedance element to said motor controller', a second motor, a second motor controller, a connection from the other end of the impedance element to said second controller, and a connection from both controllers to a center tap of said impedance element whereby adjustent of said element effects a potential drop across said impedance element and causes the operation of said motors.

9. Motor control means comprising, two bridge networks having an output member of one network connected to one of the output members of a second network, a center-tapped resistor connected across the two remaining output members of the two networks, a third bridg-e network having an output portion connected to the centertap, a first motor means including a controller, a connection from the controller to one remaining member, a second motor means including a controller, a connection from the second motor means controller tothe other remaining member and a connection from the other output portion of the third bridge to said motor means controllers all whereby a signal derived from a difference in potential across a pair of bridge outputs members in the rst or second networks causes one type of operation of said motor means and a signal derived from a difference of potential across the output portions or said third bridge causes another type of operation of said motor means.

lil. Flight control apparatus for an aircraft having two control surfaces, said apparatus comprising: separate motor means for `operating each control surface, control means for each motor means, a plurality of impedance networks having adjustable members and each network having output elements connected in series leaving tWo remaining elements constituting the output sides of the series, an impedance element connected across the output sides of said series networks and having a center tap, a connection from one end of said impedance element to each control means, and a connection from the centertap of said impedance element to each control means, whereby a signal derived from the movement of a member in one impedance network causes operation of said motor means in opposite directions to move said control surfaces in opposite directions.

11. Flight control apparatus for anaircraft having two control surfaces, said apparatus com'- prising: separate motor means for operating each control surface, control means for each motor means, a plurality of impedance networks havpedance network, a connection from one end of said impedance element to each control means, and a connection from the center tap of said impedance element to each control means, whereby7 a signal derived from the movement of either member vof said impedance networks causes operation of said motor means in opposite directions to move said control surfaces in opposite directions.

l2. Flight control apparatus for an aircraft having two control surfaces, said apparatus comprisA ing: operating means for said control surface control means associated with said operating means, a plurality of impedance networks each network having two output terminals, connections from one network terminal to another network terminal leaving two free terminals whereby the networks are electricalh7 connected in series, each said impedance network having an adjustable element, a center tapped resistor connected across the free terminals of the series connected impedance networks, a connection from one end of the resistor to one control means and a connection from the opposite end. of the resistor to the other control means, an additional impedance network, a connection from said additional impedance network to the center tap of the resistor, a connection from a movable element of said additional network to each said control means, means responsive to the difference between the heading of the aircraft and the direction of movement of the aircraft to adjust one impedance element, means responsive to the movement of the aircraft about one airis to move the element of another impedance network, and means responsive to the movement of the aircraft about another aXs for controlling the movable element of the additional impedance network, whereby movement of the elements through the change of heading device or the movement of the aircraft about one axis causes the operation of the control surfaces in Opposite directions and on the other `hand movement of the additional network element vdue to movement of the aircraft about another axis causes both control surfaces to be moved togather in the same direction.

13. In an automatic flight control system for an aircraft having two control surfaces which control the movement of the aircraft about the same axis; an operating means for each said conrol surface; a control means for each said operating means each control means including a condition responsive means, a follow up means driven by said operating means, and an individual manual means for each control means, each control means being effective to cause the operation of its operating means; said follow up means rendering said manual means and said condition responsive means ineffective with respect to said operating means pending their further operation. 1.4, Control apparatus for an aircraft having `control .surfaces for positioning said craft about the roll axis and a control surface for positioning said craft about the vertical axis, said apparatus comprising: a vane pivotally supported on said ,graft whereby it may align itself with the direction of the air relative to said craft; position maintaining means responsive to change rin position of said craft about said vertical axis; motor means for operating said roll axis surfaces; motor means for operating said vertical axis surface; combining means controlled by said vane and said position maintaining meansl for operating said roll axis surface motor means in accordance with the differential movement of said vane and position maintaining means; and means controlled by said vane for operating the vertical axis motor means in accordance with the movement of said vane.

15. Flight control apparatus for aligning the flight path of an aircraft with a heading to be maintained, said aircraft having aileron control surfaces and a rudder control surface, said apparatus comprising: a vane pivotally mounted on said craft and responsive to the side slip angle of said craft whereby it aligns itself with the direction relative to said craft heading; position maintaining means for detecting changes in heading of said aircraft; a variable signal providing control device operated by said vane in a sense and magnitude proportional to pivotal movements of the vane relative to said craft; a variable signal providing control device operated by said position maintaining means in a sense and magnitude proportional to changes in heading detected by said position maintaining means; motor means adapted to operate said aileron control surfaces; motor means adapted to operate said rudder control surface; means for combining the signals from said two control devices and connected to said aileron motor means for effecting operation of said aileron motor means upon differential operation of said two control devices; means for operating said rudder motor means from said vane operated signal providing control device, whereby if said heading signal device and side slip signal device operations are equal and of the same sense the rudder only will be operated te align the craft heading with the direction of the air relative to said craft and whereby for a differential operation of the two control devices by the vane and position maintaining means to produce a diiferential error said ailerons are additionally operated to bank said craft to align said flight path with said heading to loe maintained to remove the differential error.

16. In a night control apparatus for an aircraft having aileron control surfaces for banking the craft to change direction of craft iiight,

in combination: a iirst signal providing control means; relative Wind responsive means connected to said signal providing means and responsive to the angular direction of the craft with respect to the relative wind to adjust said signal providing means in accordance with said angular direction to provide a signal variable in sense and proportional to the magnitude of said angular direction; a second signal providing control means including a direction maintaining device responsive to and proportionally adjusted in accordance with the angle between the heading of said craft and the direction of said device for providing a second signal variable in sense and proportional to the magnitude of the angular heading deviation of said craft from the direction of said direction maintaining device; operating means for said aileron control surfaces; means including algebraic signal combining means connected to said nrst and second control means and to said operating means for controlling said operating means to effect operation of said ailerons to change the heading direction of the craft whenever said signals are not equal and opposite in sense; and means connected to and controlled by said relative wind responsive means for changing the heading of the craft in a direction tending to cause said craft to head in the direction of the relative Wind.

WILLIS H. GILLE.

References Sit-ed in the iile of this patent UNTED STATES PATENTS lurneer Name Date 1,351,538 Reynolds Aug. 31, 1920 1,777,282 Constantin Oct. 7, 1930. 1,832,334 Tarbox Nov. 17, 1931 1,839,273 Avery Nov. 29, 1932 2,159,142 Fischer May 23, 1939 2,201,174 Harding et al May 21, 1940 2,323,151 Meredith June 29, 1943 2,343,288 Fink Mar. 7, 1944 2,387,795 Isserstedt Oct. 30, 1945 2,417,821 Harcum et ai Mar. 25, 1947 2,420,932 Cornelius May 20, 1947 2,464,629 Young Mar. 15, 1949 

